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%I #17 May 29 2018 03:06:29
%S 1,4,5,9,10,21,32,34,45,55,65,68,70,129,153,160,176,183,203,245,340,
%T 370,407,441,550,580,635,741,765,806,845,965,1011,1025,1089,1166,1247,
%U 1292,1505,1508,1840,2271,2402,2584,2590,3285,3604,4065,4223,4832,5339
%N Numbers n such that sigma(n+1)=3*phi(n).
%H Robert Israel, <a href="/A067261/b067261.txt">Table of n, a(n) for n = 1..1000</a>
%p select(n -> numtheory:-sigma(n+1)=3*numtheory:-phi(n), [$1..10000]); # _Robert Israel_, May 29 2018
%t Select[Range[6000],DivisorSigma[1,#+1]==3*EulerPhi[#]&] (* _Harvey P. Dale_, Jun 11 2017 *)
%o (PARI) isok(n) = sigma(n+1) == 3*eulerphi(n); \\ _Michel Marcus_, May 29 2018
%Y Cf. A000010, A000203.
%K nonn
%O 1,2
%A _Benoit Cloitre_, Feb 21 2002
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